As the computing and communication functions of handheld computing devices become more powerful, the user interface and display elements of such devices have evolved by attempting to adapt user interface regimes developed for personal computers for use with handheld computing devices. However, this attempt to adapt prior user interface regimes has been met with various hurdles.
For instance, the majority of current handheld computing devices make use of a physical keypad for user interface. Many different implementations of physical keypads exist that vary in orientation and relationship to the device screen. However, in every case the physical keypads take up a certain percentage of the physical space of the device and increase the weight of the device. In addition to the disadvantages of size and weight, physical keypads are not configurable in the same manner as a touch screen based user interface. While certain limited forms of physical keypads currently have, on the keys themselves, configurable displays, such as eInk or OLED surfaces, to allow for reconfiguration of the keys, even in these cases, the physical layout of keys is not modifiable. Rather, only the values associated with the physical keys on the keypad may be changed.
Other methods may provide increased user configurability of physical keypads. These methods may include stickers and/or labels that can be added to keys to reference modified functions or plastic overlays on top of the keypad denoting different functional suites. For instance, the ZBoard keyboard, meant for laptop or desktop computer use, incorporates a dual layered physical keyboard which separates the keys and their layout from the connections which send signals to the machine. As such, different physical keyboard inserts for different applications can be inserted into a holder allowing full configurability such that the orientation and layout of the keys in addition to their denotation of function is configurable. This model could be extended to handheld computing devices; however, the rate at which such a modular keypad can change functions is much slower than a touch screen user interface. Furthermore, for each potential functional suite, an additional physical key layout must be carried by the user, greatly increasing the overall physical size and weight of such implementations. One advantage of a physical keypad for handheld computing devices is that the user input space is extended beyond the user display space such that none of the keys themselves, the housing of the keys, a user's fingers, or a pointing device obscure any screen space during user interface activities.
A substantial number of handheld computing devices make use of a small touch screen display to deliver display information to the user and to receive inputs from the user. In this case, while the configurability of the device may be greatly increased and a wide variety of user interface options may be available to the user, this flexibility comes at a price. Namely, such arrangements require shared screen space between the display and the user interface. While this issue is shared with other types of touch screen display/user interface technology, the small form factor of handheld computing devices results in a tension between the displayed graphics and area provided for receiving inputs. For instance, the small display further constrains the display space, which may increase the difficulty of interpreting actions or results while a keypad or other user interface scheme is laid overtop or to the side of the applications in use such that the application is squeezed into an even smaller portion of the display. Thus a single display touch screen solution, which solves the problem of flexibility of the user interface may create an even more substantial set of problems of obfuscation of the display, visual clutter, and an overall conflict of action and attention between the user interface and the display.
Single display touch screen devices thus benefit from user interface flexibility, but are crippled by their limited screen space such that when users are entering information into the device through the display, the ability to interpret information in the display can be severely hampered. This problem is exacerbated in several key situations when complex interaction between display and interface is required, such as when manipulating layers on maps, playing a game, or modifying data received from a scientific application. This conflict between user interface and screen space severely limits the degree to which the touch based user interface may be used in an intuitive manner.